For the economical use of modern production machines, their high acquisition costs demand that not only the machining time of a workpiece is restricted to a minimum, but also the downtimes of the machine. This also applies to the time for machine change-over from one workpiece to another workpiece to be machined, and means that as far as the procedure includes a tool change this must be performable with minimum time expenditure without loss in fixture accuracy.
With small tools, this demand can often be fulfilled without technical problems. It is sufficient to loosen or tighten a single screw or to trigger a single automatic clamping action, in order to unclamp the tool and then to clamp the new exchanged tool to the tool spindle, retaining the same high radial and axial runout accuracy. Such fixtures for rotary machining tools are well known in numerous engineering standards. The time expenditure for a tool change is short.
In the case of heavy and large tools, however, on account of the weight and the demands on rigidity and on repeatability with respect to the quality of radial runout, axial runout and balance of the connection between tool and tool spindle, it is often not possible to manipulate the fixture of the tool on the tool spindle by means of loosening and tightening a single screw. Such tools include, for example, the grinding worms of grinding machines for the grinding of gears.
DE 100 32 073 shows a typical example for the fixture of a grinding worm on the spindle nose of the grinding spindle of a tooth flank grinding machine by means of a taper spigot and flange screws. In order to achieve the high quality of radial and axial runout which must be demanded for reasons of production quality, and to avoid impermissible out-of-balance on the grinding spindle, a tool change requires six screws arranged symmetrically around the periphery of the grinding spindle flange to be unscrewed and, after the tool change, to be tightened uniformly in alternating sequence. This process takes a comparatively large amount of time. For the reduction of change-over effort, therefore, practical considerations demand solutions by which the time required as common to practice for the changing of a grinding worm is substantially decreased without quality loss.